The present invention relates to a rotary compressor for compressing desired gaseous fluid such as refrigerant and, more particularly, to an improvement in a rotary compressor of the type having a plurality of vanes mounted on a rotor.
A rotary compressor of the type described generally has a housing made up of a cylinder and a pair of side blocks mounted on axially opposite ends of the cylinder. A rotor is rotatably disposed in the housing and provided with vanes which are slidably received in substantially radially extending slots of the rotor. The nearby vanes define a fluid chamber in cooperation with the housing and rotor. During operation of the compressor, the rotor is rotated to cause the radially outermost ends of the vanes into sliding movement on the inner surface of the cylinder, thereby repeatedly increasing and decreasing the volume of the fluid chamber to compress incoming gas. The primary requisite in compressing gas in the manner described is that the outermost ends of the vanes be constantly held in sealing contact with the inner surface of the cylinder to fluidly isolate nearby fluid chambers. Such has been implemented by defining a back-pressure chamber by the radially innermost end of each vane and its associated slot and communicating a high fluid pressure to the back-pressure chamber. In operation, the pressure in the back-pressure chamber cooperates with centrifugal force developed in the vane in forcing the vane radially outwardly into sealing contact with the cylinder.
It has heretofore been customary to control the pressure P in the back-pressure chamber to a constant value as expressed by EQU P=1/2 (Pd+Ps)
where Pd is a delivery pressure and Ps, a suction pressure.
The problem encountered with the above prior art implementation is that during a compression stroke the pressure P becomes short to allow the vane to retract into the associated slot beyond the periphery of the rotor and, upon the subsequent suction stroke, suddently project from the slot hitting against the inner surface of the cylinder. This results in the generation of noise generally referred to as vane chattering.
To eliminate vane chattering, there has been proposed a rotary compressor of the type which makes the back-pressure chamber fluidly independent in the course of a compression stoke, as disclosed in Japanese Patent Laid-Open Publication No. 57-26293/1982, for example. Specifically, the back-pressure chamber in a compression stroke becomes an independent space so that the pressure therein may be raised against retraction of the associated vane into the slot. This type of configuration is not fully acceptable, however, since where the proportion of oil or like pressurized liquid in the back pressure chamber is substantial the vane compresses that liquid to raise the previously mentioned pressure P to an excessive level, resulting in an increase in the sliding friction between the vane and the cylinder and, therefore, a poor coefficient of performance.